SimonD

It's a pretty standard detail, not a lot you can do about it other than design the timber frame to have an external layer of insulation, which is what wood fibre is often used for. You could also bring up the eps to above the sole plate. What is your timber frame buildup as from the drawing it looks like there is something outside the timber frame before the battens and cladding?

Yes ?

The irony here is that this is exactly how the international tax system works and why we've got massive multi-national companies avoiding local taxes. It's called transfer pricing where companies allocate earnings and profits to low tax regimes, utilising various tax treaties between individual countries. Rather makes a mockery of these dearly held EU mechanisms even if the EU is trying to clamp down on this practise. I'd hazard a guess that the Brexiteers thought they could implement a similar system with Brexit and trade agreements, but who knows...

It is a weird thing and as @SteamyTea says, when it's about investor speculation, it's just one facet of rentier capitalism - if you've got the money you buy up finite or in demand natural resources and then restrict supply for your own income. However, there is a contract where they do technically buy the commodity, it's just agreed at a specific date in the future. The contract is then settled either with the actual product or cash, but the contact can be bought and sold anytime until the contract is due as the value of the contract varies, so it's a popular way for traders to make money. During the pandemic oil futures went into negative territory because those who had futures couldn't sell the contract, or the oil, so would be hit by huge storage costs and were offering to pay to get rid of the contract.

Ply doubles up as vcl in this buildup. Agree with other comments re 9mm as the board for epdm. I'd suggest considering using the 9mm play on the inside of the roof (unless that's already planned) and then either doubling up as @TonyT suggests or getting in either osb or ply in 18mm.

I think all our timber supplies were decimated during WW2 and never replanted enough so we've had to rely on imports for timber. I read an article fairly recently that UK timber plantation owners were preferring to limit local supply because the capital value of the plantations was comfortably increasing year on year, making a good investment. I wonder whether, with the current lumbar prices, we might see a wave of local British timber hitting the market....

For me it's interesting that those 2 are also traded as commodities where their futures values have rocketed recently as have all raw materials. Unfortunately this can decouple their value from mere supply/demand because the high values attract investors looking to make a quick buck, which of course inflates their value even more, producing an unpleasant inflationary cycle. As you say, it's interesting that construction isn't back to full steam yet. According to this article https://www.building.co.uk/data/market-forecast-high-hopes/5111690.article construction output is still below pre-pandemic levels. Another point the article mentions is that infrastructure projects are maintaining demand. Something else I came across was that supply capacity hasn't been keeping pace with demand for a good 10 years or so, thus we already had a foundation of a constant upward trend in materials prices. I suspect that as recovery continues, we're actually going to see further problems with supply and thus price inflation, and some opinion suggests it's going to continue for at least a year or so.

Yikes, that's expensive! But yes, OSB supply is a problem. Is the pine plywood you've been offered definitely a structural grade? Probably Elliottis pine if it is, I'd guess. The pine plywood should be fine for sheathing, it's been used for donkeys for sheathing. The only times you need to worry about mould is if the moisture content in the wood becomes too high, but then you're likely to get problems with the osb too. If your shed is built right, it'll be dry enough and ventilated enough so no need to worry. Don't whatever you do put that vapour barrier you linked to above on the outside. You need a breather membrane. Your builders merchant should have something on the shelf that'll do the job. I'd recommend you go for 100mm insulation at least. HTH.

A few weeks ago it was £240 + VAT for grab up to 18t for us - Bristol/North East Somerset area.

My sister used Wiltshire building control for a project and it was fine, no problems there.

I've recently received an expensive front door which is 2.1m high by 1.2m wide. I'd seriously thought about making it myself but my wife talked me out of it. I'm glad she did. Ours is made with Accoya and is well insulated. I has a steel reinforcement frame, necessary due to its size, plus multi-point locking etc. The door weighs 107kg. It's also manufactured as a door set with inset heavy duty hinges, three at the top, one at the bottom. Overall, I wouldn't have managed anything even remotely close to this and I do think it takes a lot of skill (and tooling) to produce something like this diy that will last.

I kind of meant it in jest but there was a more practical undertone. Since self-building, my head has been so full of questions and information on how to get it right, there's no room for how not to do it. But in any case, if you want to learn how to do something well, it's surely better to spend your time listening to and watching someone who's good at it, not someone who's crap at it, no? Understanding how not to do something doesn't get you anywhere, other than maybe some entertainment value from other peoples' disasters. ?? I haven't watched one of these programmes in probably 10 years now but one thing I did always wonder was how on earth so many people seemed to find an extra 300 - 500 grand or so behind the sofa to complete the project....

Stop watching Grand Designs (or any other self-build programme) ?, spend some time learning how to make decisions and save up your money. Think about how much of the work you want to do and then try to develop any necessary skills and some experience ahead of time - or not if you want to pay someone else to do it all; then you can sit back, drink beer and consume design inspiration ? Otherwise I'd just be repeating what others have said..

Those seem like good prices at the moment and they have availability. My local timber merchant said they can't get osb until maybe June sometime. Having just looked it up, it's interesting that price difference is now only a few quid between chipboard, osb and ply (I know, I'm slow on the uptake ? ). I've not used Radiata pine plywood yet but by all accounts its quality is up there with the usual European stuff - however, I'm off to a specialist plywood supplier later this week to look at samples of some other Chilean plywood for furniture making. If you like, I can report back on that visit if there's anything helpful in what I find.

Yes, context is important, I agree. That said, it won't always end up with additional cost and wastage. E.g. at 400 c/c the equation changes. I don't know what board pricing is right now but last I received comparative quotes for Egger v osb, the osb was significantly cheaper. My approach would be to use the materials most suitable to the situation and design. A developer or contractor will no doubt approach it all differently to a one man self-builder. I lay out the board arrangement in CAD first to know how the boards will work. The last time I calculated and boarded a floor @ about 100sqm I ended up with less than 3 boards in total wastage as off cuts and zero noggings. The last time I left it to builder & supplier, I ended up with 4 boards extra from an approx 12sqm room including noggings..

I disagree. It's just as suitable for modern floor systems. You'll typically still frame posi and JJI joists at either 400 c/c or 600 c/c (or 16" and 24" c/c), so there's no problem there, other than with a little measurement and lining up the board properly at the start of a run. No big deal. If you really need noggins with posi and JJI, I think in many cases it's easier as you're clipping and nailing these to the top flange, just as you would to support a partition wall with these systems. Alternatively you can use full depth LVL or timber with packers and full depth blocking. James Jones have a great technical library illustrating all these details https://www.jamesjones.co.uk/assets/uploads/assets/downloads/brochures/site-guide-floors-3rd-sept-20.pdf

Wow, plywood used to be about 2.5 times the price which is why I went with osb. I'd go for plywood without any worry.

Yes, of course, but isn't that the case with any floor board? And surely you'd frame your floor to avoid that problem.

18mm OSB only needs support at short ends on joist, no extra framing required.

I missed that. Yes, not great. I've come across uk framers who believe that if you tape the insulation joints you don't need a vcl - I've also seen it approved by building control.

Why are you looking for 22mm? The 18mm osb is at least 'equivalent' to a 22mm P5 and good for 600mm c/c. I think the only times 22mm is used is in commercial projects and I suspect special order only.

Interesting video. At about 5:50 there's a picture of the stud wall with an octo-stud arrangement! It looks like some of the studs are sistered but surely the timber frame company could have found a more efficient solution?

Tapcon screws are good for this. For your timbers you'd need the 82mm length: See https://www.metrofixings.co.uk/main/product/productinfo/606/5 x 82mm 3F82 Countersunk Concrete Screw/1 Installed at 400 centres should work fine. You just drill a hole, clean out the hole and screw them in. For belt and braces you could add some straps. The first method you mention is the traditional way of building modern stick timber frames. Frankly for a workshop, I don't think it matters that much. However, if it's going to be insulated and possibly heated then with the OSB on the inside, this creates your vapour control layer (providing you tape all the junctions and corners between the sheets) that prevents too much moisture entering the frame from the inside of the building. Then, as your builder has said, you just need a breather membrane to the outside. If you go for the osb around the outside, you'll need a vapour control layer - anything from a thin plastic sheet to advanced adaptable membranes - in the inside of the frame. You'll also need a breather membrane on the outside of the osb. So in a way, osb on the inside can be easier. If you're planning to insulate and have it heated, especially with blown cellulose, you need to get the detailing right on the wall buildup to take the pressure of the pumped insulation, but the osb on the inside should be fine. I'd also suggest that if it's to be heated and you insulate with something wooly, I'd counter batten the outisde of the frame with 2x2 and install an extra layer of insulation. Using cheapo glass wool insulation this will be as cheap as chips. It'll take the edge off the cold on winter and help a bit in the summer. So basically you'd end up with a wall build up from the inside: osb stud wall 2x2 cross battens breather membrane battens for cladding cladding. I would line the inside of the roof structure with osb - to act as your vapour barrier, just like with the walls. With the metal roofing sheets you are going to get condensation on the inside. You must make sure you have a ventilation gap between your insulation and the metal roof. So I'd recommend you plan in battens on top of the rafters. With or without insulation, I'd install a breather membrane on top of your rafters, under the battens. Essentially you'd end up with a buildup along these lines from the inside: osb rafters (with insulation) breather membrane battens (forming ventilation gap) roof sheet As with the walls, it's worth considering the thickness of your rafters and the amount of insulation you can get in there. Just make sure your rough opening are straight and true, ? and a bit larger than your windows and doors. 10mm each side/top & bottom usually works fine. There are plenty of sites that'll show you how to frame rough openings but here is one that covers it https://www.jlconline.com/training-the-trades/framing-rough-openings_o The great thing about timber framing is that you can actually still do most of it with hand tools. All you really need is: Hammer Screwdriver Hand saw Pencil Tape measure Square (speed square is ideal) Spirit level Chisel (Stapler for membrane helps) String (for straightening frame and walls) But you'll need a drill for your sole plate and anchors.. Good luck with it!

I completely agree. I have 18mm OSB and density has never been a consideration by anyone. It's only the structural performance of the board that's ever been considered. It's worth keeping in mind that, as @Moonshine suggested, the building regulations aren't entirely prescriptive and you've got detailing options, often provided by materials manufacturers.

To put the board density question into perspective, I've just bought a load of Knauf Aquapanel Outdoor - the given density for this board is 16kg/m2. Is there actually a timber based board that doesn't contain cement that gets up to 15kg/m2 without a silly thickness?